1. Field of the Invention
The present invention relates to a reversible thermosensitive recording medium.
2. Description of the Related Art
IC cards incorporated therein with an electronic information module including an IC chip (electronic information recording element) and an antenna circuit have been introduced in various industries, such as cash cards, credit cards, pre-paid cards; cards used for public transport, such as railway, bus, and motor way services; member's cards for digital broadcasting services, or 3G mobile phone services; and cards such as library cards, student cards, employee ID cards, and resident registration cards; and have been used in various field from use in every day life to business use.
Meanwhile, paper has been still used for work sheets, and instructions (e.g., a parts control manifest, and a process control manifest), which are larger in size than a card. Along advancement of economic social activities, such as mass production, mass consumption, and mass disposal, therefore, there are problems that quantities of paper produced, consumed, and disposed increases, and as a result, load to the environment increases.
Accordingly, there is a need for a recording medium having a larger size than the card incorporated therein with an electronic information module, using the technology of the IC card.
Even with the IC cards, the disposal amount thereof cannot be suppressed unless they can be repeatedly used. Accordingly, there is a need for reducing consumption of resources and reducing environmental load by promoting effective use or recycling of resources.
There is disclosed use of a reversible thermosensitive recording medium as the IC card, and the reversible thermosensitive recording medium to which the electronic information recording module is incorporated, and which has a reversible thermosensitive recording layer in which a visible image can be formed and erased. Use of the reversible thermosensitive recording medium can reduce the disposal amount of the IC cards, as the reversible thermosensitive recording medium can display recorded information as a visible image as well as rewriting internal information of the IC chip, and can repeatedly used.
The IC cards may be broken, or cause troubles during use thereof. In such a case, a manufacturer determines the production date and production lot of the IC card, and then researches the production history of the relevant lot, investigates a fault defect, and investigates an influence to other lots produced on the same production date, and the same process number.
Conventionally, as for a method for determining the production date or production lot of the IC card, a method for marking (numbering) characters on a front or back surface of the IC card has been used. Specifically, examples thereof include: an embossing method, in which a character pattern is embossed against a surface of a card so that a mark appears three-dimensionally on the surface of the card; a thermal transfer method in which a transfer leaf is thermally transferred onto a surface of a card by means of a thermal head; and a laser marking method, in which a portion of a surface of a card is burned and removed by laser.
In the case where the reversible thermosensitive recording medium is used for the IC card, however, troubles may be caused with the reversible thermosensitive recording medium when a mark is formed by the embossing method or thermal transfer method. The reversible thermosensitive recording medium is typically, subjected to formation or erasure of an image in a reversible thermosensitive recording layer by means of a heating device of a printer, such as a thermal head, an erasure bar, an erasure roller, and an erasure plate, after the marking. In the case where formation or erasure of an image in the reversible thermosensitive recording layer is performed by the heating device after the mark is formed by the embossing method, there is a problem that a printing failure or erasing failure occurs. In the case where formation or erasure of an image is repeatedly performed on the reversible thermosensitive recording layer by the heating device after the mark is formed by the thermal transfer method, there is a problem that the transfer leaf starts to peel off.
Accordingly, as the method for forming a mark in the reversible thermosensitive recording medium, the laser marking method is preferably used (see Japanese Patent Application Laid-Open (JP-A) No. 2008-262527).
As the laser marking method, there have been known a technique for forming a mark, which has high contrast to the background, and is hardly impaired in terms of a shape of a character, on a card-type information recording medium (see JP-A No. 2004-110581), a technique for forming a laser mark (groove) in a non-transparent layer of a card-shaped recording medium having the non-transparent layer on a front or back surface of a base material, to the extent where a surface of the under layer on which the non-transparent layer has been formed can be visually observed (see JP-A No. 2003-127570); and a technique for laser marking a surface of a card base material to give a depth of 15 μm or less (see JP-A No. 2006-201901).
In any of these techniques, however, there are problems that visibility of the mark is not sufficient. Further, these techniques are not directed to a reversible thermosensitive recording medium, and cannot be used repeatedly, hence cannot solve the problem of the environmental load.
The present inventors have found a new problem that, when an image is formed in a reversible thermosensitive recording layer after laser marking a reversible thermosensitive layer, which has the reversible thermosensitive layer on a base, and a laser mark is to be formed in a surface of the base opposite to the surface thereof on which the reversible thermosensitive recording layer has been formed, missing image (white missing part) is left and a printing failure occurs in an area of the reversible thermosensitive recording layer, which is a corresponding area on the opposite side of the laser mark. Further, it has been found that the white missing part becomes more significant after repeated use of the reversible thermosensitive recording medium. In the case where the reversible thermosensitive recording medium cannot be used repeatedly, it is disadvantageous in terms of a cost, because the reversible thermosensitive recording medium has an electronic information recording module, which is an expensive member.